Mainlines do read lower due to their more accurate correction factors but this is widely know, so you can compare DD figures to DD amd mainline to mainline but can't really compare them against eaach other.
I fitted the exhaust and cooler to this car, there was also some cat "modifications" so the boost increase is due to the increase in the exhaust flow.
The boost reading is off the MAP sensor on the exhaust.
I would say that the figure is pretty accutre due to how i only just pulled away in my lighter 180 which was running about 205kw(14.5psi) at the time when we had a run on the freeway on the way to Mallala (kept it under 110 of course).
As cubes and Jeff said prehaps it's just a freek.